Funds are requested for a mass spectrometer system, composed of a ThermoFinnigan LCQ Deca XP Plus ultra sensitive MS n ion trap mass spectrometer and atmospheric pressure MALDI ion source, with a nanoliter flow HPLC capable of two-dimensional chromatography. This instrument system provides high sensitivity and mass accuracy with tandem mass spectrometry capabilities. It is ideally suited for proteomics applications, characterization of macromolecular assembles, and identification of patterns of biomarkers and potential therapeutics in technology transfer applications. Thirteen groups of investigators participate in this proposal, which includes projects in understanding the mechanisms of obesity, meiosis, signal transduction, HIV/AIDS, infectious diseases and cancer. The instruments will be operated and supervised by experienced mass spectrometrists and protein chemists within an existing shared protein core facility with a record of productivity and collaborative interactions.